Dead arm is the name of a grapevine disease that has all but been phased out, since it was discovered that what was thought to be one disease was, in fact, two. It is now commonly accepted that these two diseases should be diagnosed and treated separately, but since the name “dead arm” still comes up in literature, we will examine it here. Keep reading to learn more about recognizing and treating dead arm in grapes.
Grape Dead Arm Info
What is grape dead arm? For about 60 years, grape dead arm was a widely recognized and classified disease known to affect grapevines. Then, in 1976, scientists discovered that what had always been thought to be a single disease with two distinct sets of symptoms was, in fact, two different diseases that almost always appeared at the same time.
One of these diseases, Phomopsis cane and leaf spot, is caused by the fungus Phomopsis viticola. The other, called Eutypa dieback, is caused by the fungus Eutypa lata. Each has its own distinct set of symptoms.
Grape Dead Arm Symptoms
Phomopsis cane and leaf spot is usually one of the first diseases to appear in the vineyard’s growing season. It manifests as small, reddish spots on new shoots, which grow and run together, forming large black lesions that can crack and cause the stems to break off. Leaves develop yellow and brown spots. Eventually, fruit will rot and drop off.
Eutypa dieback usually shows itself as lesions in the wood, often at pruning sites. The lesions develop under the bark and may be hard to notice, but they tend to cause a flat area in the bark. If the bark is peeled back, sharply defined, darkly colored lesions in the wood can be seen.
Eventually (sometimes not until three years after infection), the growth beyond the canker will begin to show symptoms. This includes stunted shoot growth, and small, yellowed, cupped leaves. These symptoms may disappear in midsummer, but the fungus remains and the growth beyond the canker will die.
Grape Dead Arm Treatment
Both diseases that cause dead arm in grapes can be treated by application of fungicide and careful pruning.
When pruning vines, remove and burn all dead and diseased wood. Leave only obviously healthy branches. Apply fungicide in the spring.
When planting new vines, choose sites that receive full sunlight and lots of wind. Good airflow and direct sunlight go a long way in preventing the spread of fungus.